Biphenyl is a benzenoid aromatic compound that consists of two benzene rings connected by a single covalent bond. Biphenyl occurs naturally in coal tar, crude oil, and natural gas. Formerly used as a fungicide for citrus crops. It has a role as an antimicrobial food preservative and an antifungal agrochemical. Biphenyl is used in organic syntheses, heat transfer fluids, dye carriers, food preservatives, as an intermediate for polychlorinated biphenyls, and as a fungistat in the packaging of citrus fruits.

1. E. I. du Pont de Nemours and Company technical product, m.p. 111–112°, was used.

2. The time required for the addition varies from 1.5 to 2 hours.

3. There must be an excess of sodium carbonate to prevent the troublesome frothing caused by the liberation of carbon dioxide near the end of the coupling reaction.

4. The addition must be regulated so as to prevent the formation of large chunks of sodium carbonate decahydrate.